Depending on their structure, standing bodies of water have different typical species populations. Pools are small, very shallow bodies of water. They dry out during hot summers. As a result of the lack of depth, the water temperature can rise rapidly in locations exposed to the sun. These assumed limitations give rise to a need for specially adapted animal and plant species. A woodland pool (Waldtümpel) is a special form of a pool. In these cases the temperature rises more slowly in spring and cools less rapidly in the autumn.
Heavy rainfall or melting snow in the spring generally play a part in creating these pools. Pools also form in the vicinity of springs. Because of their intermittent nature, pools are free from fish. There is therefore scarcely any predatory pressure on the larvae of amphibians or insects. Pools often owe their origin (and in the Life project area, mostly) to man-made depressions in the ground. Some extremely small standing bodies of water are caused by the ruts made by agricultural and forestry machinery. These are to be found everywhere in the Life project area and represent the primary habitat of the yellow bellied toad (Bombina variegata).
Larval development is accelerated by the rapid warming in the spring and therefore ideal breeding conditions for rare amphibian species such as the yellow bellied toad predominate. These parts of the countryside which create diversification therefore also offer welcome habitats for aquatic plants, e.g. for endangered colonies of pygmy rushes (nanocyperion).
In the last 50 years between 70 and 85% of all pools were filled in. They owe their status as an undesirable part of the countryside primarily to their characteristic as a hindrance to farming. They also act as ideal pools for the breeding of gnats and mosquitoes. Filling in these minor pools also deprived rare species such as the yellow bellied toad of their habitat.